Project Summary: Texas Children's Hospital (TCH) aims to establish an inpatient and emergency department surveillance site as part of the larger national New Vaccine Surveillance Network (NVSN) to assess the burden of pediatric respiratory and gastrointestinal illnesses in hospitalized children and children seeking care in the emergency department. Specifically, we will assess the burden of influenza and assess the vaccine effectiveness (VE) against laboratory-confirmed influenza infections among hospitalized children <18 years of age during influenza season. We will also operate year-round surveillance of other non-influenza pathogens, including but not limited to respiratory syncytial virus, human metapneumovirus, parainfluenza virus, rhinovirus, and emerging respiratory pathogens, such as enterovirus D68, in children <5 years of age. In addition, we will assess the burden of other gastrointestinal pathogens such as norovirus and adenovirus. TCH is an ideal site for surveillance due the large number of admissions each year (>39,000), racial and ethic diversity of the Houston area, and the similarity of the TCH population to that of the community. Nasal and throat swabs will be collected from all subjects and tested for a wide-array of viral pathogens using molecular methods in the laboratory of Dr. Piedra, a national expert in pediatric respiratory disease. Stool specimens will undergo molecular testing in the TCH clinical laboratory for a wide-array of pathogens. Children who test positive for influenza, or other viruses, will be compared with children who test negative for influenza, or other viruses, and healthy (control) children who present to Texas Children's Pediatrics practices for well- child care. Complete vaccination histories will be obtained for all children and influenza VE will be calculated. The large number of children admitted to TCH with influenza (100->300 annually) will permit VE assessments by specific strain of influenza, vaccine type (live vs. inactivated), and patient age. In addition, a birth cohort longitudinal study (optional component) will build a valuable repository of maternal and infant samples and contribute to the understanding of the natural history of ARI and AGE illnesses in early life, the interaction of maternal and infant pathogen exposure and immunity, and the assessment of host, pathogen and environmental factors, including immunization, in the infant's risk for infection and severity of disease.